The present invention relates generally to hydraulic devices, and more particularly to the inclusion of an anti-stiction feature between a moveable component and body of a hydraulic device.
Many hydraulic devices include a hydraulically driven piston assembly, which in its most basic form is made up of a barrel and a movable piston. In many instances, including hydraulic systems associated with internal combustion engines, the hydraulically driven pistons must have the ability to operate over a wide range of temperatures. In some cases, such as when the actuating fluid is engine lubricating oil or the like, the fluid can become extremely viscous toward the low temperature operating range of the hydraulic device. For instance, in the case of hydraulically actuated fuel injectors, the devices should have the ability to operate at relatively low temperatures, such as when the engine is undergoing a cold start.
In those cases where a large portion of the piston hydraulic surface comes in contact with the barrel when in its retracted position, a sticking phenomenon can occur, and acts to inhibit or delay the ability of the piston to break free even in the presence of high pressure actuation fluid. In other words, a relatively thin but highly viscous fluid layer between the piston and the barrel can cause the piston to resist breaking free to perform an activation event, such as pressurizing and injecting fuel in the case of a hydraulically actuated fuel injector. The result of this phenomenon is to require excessive and sometimes annoying engine cranking before the pistons within the fuel injectors can break free and cause fuel to be injected in order to start the engine.
In addition to potential sticking problems associated with intensifier pistons in hydraulically actuated fuel injectors, potential sticking can also occur at other locations within such fuel injectors. For instance, if the fuel injector includes a direct control needle that includes a needle piston exposed on one side to oil, movement of the needle piston can become sluggish and/or briefly stuck when it comes in contact with its stop. In addition, some fuel injectors of this type include a pilot operated control valve that may include a ball and pin pilot valve operably coupled to a spool valve member. Because the spool valve in many of these control valve assemblies is hydraulically driven and comes in contact with a stop surface, its performance can also become sluggish and/or become stuck against its stop surface. Finally, in the case of a ball and pin pilot valve, the armature of a solenoid that is coupled to the pilot valve ball and pin can have a position where it comes in contact with a stop. If the area in and around the armature is wetted with oil, the same sticking and/or sluggish response behavior can again reveal itself.
Although hydraulic systems have long been known in many different art fields, it is believed that the problem of sluggish performance and/or sticking primarily only occurs in hydraulic systems, such as fuel injectors, that include relatively small, light weight components that move within a body over relatively small distances, and must move very quickly for the device to perform properly.
The present invention is directed to these and other problems associated with component sticking in relatively high viscous environments.
In one aspect, a hydraulic device includes a body with a first surface and a component with a second surface moveably positioned in the body. In a first position, the component is in contact with the first surface of the body over a contact area. In a second position, the first surface is out of contact with the second surface. An improvement includes making the contact area a portion of at least one thin raised surface feature on one of body and the component.
In another aspect, a hydraulic device includes a body and a component moveably positioned in the body. A separator is in contact over a contact area with at least one of the body and the component when the component is a retracted position. The separator is out of contact with at least one of the body and the component when the component is away from its retracted position. A contact area is a portion of a substantially smooth surface on one of the body and the component. The contact area is located away from the centerline and/or less than 15% of the area of the substantially smooth surface.
In still another aspect, a method of reducing sticking in a hydraulic device includes a step of providing a body with a movable component therein. The component has a second surface in contact over a contact area with a first surface of the body when in a first position. When in a second position, the first surface is out of contact with the second surface. One of the first surface and the second surface are positioned atop a raised surface feature, and the other of the first surface and the second surface is part of a substantially smooth surface. The contact area is sized and arranged to be at least one of thin and/or less than 15% of an area of the substantially smooth surface.